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TPA3112D1: Class D amp Conducted emissions

Part Number: TPA3112D1
Other Parts Discussed in Thread: TPA3138D2, TPA3136D2

I have recently designed an Audio player using the TPA3112D1.  I copied the reference design as close as possible. I am using a 24V power supply.  Everything works as correctly, however I am failing the FCC test for conducted emissions, with 340khz and its harmonics causing failure.  I have traced this to the audio amplifier, as it starts as soon as the amp is unmuted, as is mostly dependent of audio power levels.  I am a bit puzzled what to try here.

The TPA3112D1 eval module says it passed FCC, but doesn't specifically say it passed conducted emissions.  Is the full test report and setup photos available for this module?

This is my question

  • Hi Erik,
    From your SCH, you are not using inductor + cap in the output filter. With LC output filter, it can pass CE test very easily. How much is the output power? If it's larger than 10W, we recommend to use LC filter instead of ferrite bead + cap filter. If it's lower than 10W, please try to use higher impedance ferrite bead (e.g. 300ohm@100MHz) for L4/L5 and use 2.2nF cap for C57/C58. Another thing you can try is to insert ferrite bead or C-L-C PI fitler on the PVCC net to suppress the EMI.
    I recommend to use TPA3136D2 or TPA3138D2 in this application. These two devices can be set to PBTL mode to support mono outout mode, and they are optimized for much better EMI perfomance and they are p2p compatible to TPA3112D2.
    Best regards,
    Shawn Zheng
  • Our target output power is 20W.

    Is this a correct assumption that if the output filter isn't set up correctly that the device will radiate out of PVCC?

    Do you mean they are p2p compatible with the TPA3112D1 or 2 ?

  • Hi Erik,
    Your understanding is correct. Output filter plays very important role in the EMI performance. And sorry for confusion, I mean TPA3112D1. They are almost p2p(not totally), but I believe they can be used in PPBTL mode to replace TPA3112D1 on the board.
    Best regards,
    Shawn Zheng